The present invention relates to arrays of optical fibers and, more particularly, to optical fiber ribbons.
Optical fiber ribbons are used to transmit telecommunication, computer, and data information. The general structure of an optical fiber ribbon, and the materials and processing variables applied in the manufacture of an optical fiber ribbon can play a significant role in how an optical fiber ribbon will perform in the field. Optical fiber ribbon structures can be generally classified into two general categories, namely, ribbons without subunits and ribbons including subunits. A ribbon/subunit design typically includes a subunit with at least one optical fiber surrounded by a subunit matrix that, in turn, is surrounded by a common matrix that also surrounds at least one other subunit.
An optical fiber ribbon without subunits can present problems for the craft. For example, when separating optical fiber ribbons that do not contain subunits into optical fiber subsets, the craft must use expensive precision tools. Moreover, connectorization/splice procedures can require inventories of specialized splice and closure units/tools for the various subsets of optical fibers. Where the craft elects to separate the optical fiber ribbon into subsets by hand, or with a tool lacking adequate precision, stray optical fibers can result. Stray optical fibers can cause problems in optical ribbon connectorization, organization, stripping, and splicing.
An exemplary optical fiber ribbon 1 is shown in FIG. 1. Optical fiber ribbon 1 includes subunits 2 having optical fibers 3 disposed in a subunit matrix 5 and surrounded by a common matrix 4. Optical fiber ribbons having subunits can have several handleability advantages, for example, improved separation, and avoidance of stray fiber occurrences. However, one handling concern is the potential formation of wings W (FIG. 1) during hand separation of the subunits. This can be caused by a lack of sufficient adhesion between common matrix 4 and subunit matrix 5. The existence of wings W can negatively affect, for example, optical ribbon organization, connectorization, stripping, and splicing operations by the craft. Additionally, wings W can cause problems with ribbon identification markings, or compatibility of the subunit with ribbon handling tools, for example, thermal strippers, splice chucks, and fusion splicers.
Organic materials of the ultra-violet light curable (UV curable) type, and visible light curable type, have been developed for use as a base resin for subunit and common matrices. UV curable materials are generally tough, exhibit high resistance to abrasion, perform well when under stress, and are adaptable to mass production processes. When cured, a UV curable subunit matrix typically has a modulus of about 109 Pa, and a UV curable common matrix typically has a relatively lower modulus of about 107-109 Pa.
The curing of a UV radiation-curable composition suitable for use as a subunit or common matrix material is essentially a polymerization of the UV curable material, whereby the material undergoes a transition from a liquid to a solid. Prior to application to an optical fiber or a subunit, the UV curable material comprises a mixture of formulations of liquid monomers, oligomer xe2x80x9cbackbonesxe2x80x9d with, e.g., acrylate functional groups, photoinitiators, and other additives. Photoinitiators function by: absorbing energy radiated by the UV or visible light source; fragmenting into reactive species; and then initiating a polymerization/hardening reaction of the monomers and oligomers. The result is, in general, a solid network of crosslinking between the monomers and oligomers that may include fugitive components after cure. The photoinitiator therefore begins a chemical reaction, that promotes the solidification of the liquid matrix to form a generally solid film having modulus characteristics.
A key to the curing process is the reaction of a photoinitiator in response to UV radiation. A photoinitiator has an inherent absorption spectrum that is conveniently measured in terms of absorbance as a function of the wavelength of the radiated light. Each photoinitiator has a characteristic photoactive region, i.e., a photoactive wavelength range (typically measured in nanometers (nm)). Commercially available photoinitiators may have a photoactive region in the vacuum ultra-violet (VUV) (160-220 nm), ultra-violet (UV) (220-400 nm), or visible light (V-light) (400-700 nm) wavelength range. When the material is irradiated by a VUV, UV or V-light lamp, that emits light in the photoactive region, the material will cure.
In the application of a UV radiation curable material as a subunit or common matrix, light intensity and cure time are factors by which the resultant modulus of the film can be controlled. The light dose, i.e., the radiant energy arriving at a surface per unit area, is inversely proportional to line speed, i.e., the speed the radiation curable material moves under a radiation source. The light dose is the integral of radiated power as a function of time. In other words, all else being equal, the faster the line speed the higher the radiation intensity must be to achieve adequate curing. After a radiation curable material has been fully irradiated, the material is said to be cured. Curing occurs in the radiation curable material from the surface closest to the radiation source. The cured upper surface of the film can block light from reaching less cross-linked portions of the material beneath the surface. In this manner, a cure gradient may be established. Depending on the amount of incident light, a cured material may therefore exhibit different degrees of cure, and the degrees of cure across the depth profile a film can have distinct modulus characteristics associated therewith.
Thus the degree of cure affects the mechanical characteristics through the cross link density of the material. For example, a significantly cured material may be defined as one with a high cross link density for that material, and may, for example, be too brittle. Further, an undercured material may be defined as one having a low cross link density, and may be too soft, possibly causing an undesirable level of ribbon friction.
Optical fiber ribbons with subunits and a common matrix with general modulus characteristics may define a backdrop for the present invention. For example, EP-A-856761 discloses a ribbon having a common matrix surrounding discrete single-fiber optical subunits each including a respective subunit matrix. Each subunit matrix includes six tension wires formed of aramid fiber, glass fiber, or steel. The modulus of the common matrix can be set lower than that of the subunit matrix. This design is disadvantageous because the tension wires are expensive, add thickness and stiffness to the ribbon as a whole, and can present significant manufacturing difficulties. Moreover, single-fiber subunits have limited transmission capabilities.
In addition to surrounding single-fiber subunits, the common matrix can have a high modulus thereby defining a relatively rigid protective outer layer. For example, EP-A-843187 discloses a ribbon having a multi-layer common matrix with an outer protective layer. The layers of the common matrix have differing rigidness characteristics. The common matrix can have a modulus of 5 to 100 kg/mm2, and the subunit resin layer can be the same material as the common matrix. A rigid outer layer is also discussed in an International Wire and Cable Symposium paper entitled xe2x80x9cANALYSIS OF A MODULAR 24-FIBER RIBBON FOR THE DISTRIBUTION NETWORKxe2x80x9d (1998). The ribbon discussed therein includes a pair of subunits surrounded by a common matrix. The common matrix is more rigid than the subunit matrix for strengthening the structure of the ribbon. In addition, protective matrix layers with a relatively high modulus are disclosed in JP-A-80-62466 and JP-A-91-13773.
Moreover, the common matrix can exhibit predefined friction characteristics. For example, EP-A-822432 discloses a pair of subunits surrounded by a common matrix including a base resin material having a functional group of low compatibility dispersed therein. The functional group forms discrete domains of about 5 microns in diameter in the common matrix. The domains have a low modulus relative to the base resin of the common matrix for lowering the coefficient of friction (COF) of the common matrix. Another example of a COF effect is disclosed in U.S. Pat. No. 5,524,164, wherein part of the optical fiber ribbon includes a component of poor compatibility forming a discontinuous phase having a low modulus in the outer resin layer surrounding a pair of subunits. The component of poor compatibility is intended to migrate to the ribbon outer surface for reducing sliding friction.
One aspect of the present invention involves an optical fiber array comprising at least one subunit including at least one optical fiber therein surrounded by a respective subunit matrix. A common matrix is disposed adjacent to the at least one subunit, and an interfacial zone between said subunit and common matrices is defined by an adhesion treatment, the adhesion treatment comprising at least one interfacial substance having an interface characteristic in a range from an essentially non-coupled relationship to a loose bond so that the common matrix can be removed from the subunit matrix intact leaving unbound subunits.
Another aspect of the invention relates to a method of manufacturing an optical fiber array comprising the steps of:
(a) supplying at least one subunit including at least one optical fiber therein surrounded by a respective subunit matrix;
(b) creating a common matrix adjacent to the at least one subunit; and
(c) forming an interfacial zone between the common and subunit matrices by application of an adhesion treatment, the adhesion treatment comprising at least one interfacial substance having an interface characteristic in a range from an essentially non-coupled relationship to a loose bond so that the common matrix can be removed from the subunit matrix intact leaving unbound subunits.